U.S. patent application number 15/894368 was filed with the patent office on 2019-08-15 for silicon (si) modified li2mno3-limo2 (m=ni, mn, co) cathode material for lithium-ion batteries.
This patent application is currently assigned to GM GLOBAL TECHNOLOGY OPERATIONS LLC. The applicant listed for this patent is GM GLOBAL TECHNOLOGY OPERATIONS LLC. Invention is credited to Raghunathan K, Leah NATION, Yan WU.
Application Number | 20190252671 15/894368 |
Document ID | / |
Family ID | 67400178 |
Filed Date | 2019-08-15 |
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United States Patent
Application |
20190252671 |
Kind Code |
A1 |
WU; Yan ; et al. |
August 15, 2019 |
Silicon (Si) Modified Li2MnO3-LiMO2 (M=Ni, Mn, Co) Cathode Material
For Lithium-Ion Batteries
Abstract
A lithium ion battery has a positive electrode or cathode having
a silicon modified mixed metal oxide including a compound having
empirical formula
Li[Li.sub.yMn.sub.a-xSi.sub.xM.sup.III.sub.bM.sup.II.sub.c]O.sub.2
(I) wherein y=0.01-0.33; x=0.001-0.15; a, b, and c are each greater
than zero; M.sup.III is a trivalent metal or a combination of
metals with an average valence of +3; M.sup.II is a divalent metal
or a combination of metals with an average valence of +2; and
y+4a+3b+2c is equal to 3 or about 3. Such a silicon modified mixed
metal oxide may be exemplified by formula: Li [Li.sub.0.2
Mn.sub.0.49 Si.sub.0.05 Ni.sub.0.13 Co.sub.0.13]O.sub.2.
Inventors: |
WU; Yan; (Troy, MI) ;
NATION; Leah; (Cambridge, MA) ; K; Raghunathan;
(Troy, MI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
GM GLOBAL TECHNOLOGY OPERATIONS LLC |
Detroit |
MI |
US |
|
|
Assignee: |
GM GLOBAL TECHNOLOGY OPERATIONS
LLC
Detroit
MI
|
Family ID: |
67400178 |
Appl. No.: |
15/894368 |
Filed: |
February 12, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C01P 2006/40 20130101;
H01M 4/525 20130101; C01P 2002/82 20130101; C01P 2004/03 20130101;
H01M 2004/028 20130101; C01B 33/20 20130101; C01P 2002/72 20130101;
H01M 4/131 20130101; C01G 53/50 20130101; H01M 10/0525 20130101;
C01P 2002/54 20130101; H01M 4/505 20130101 |
International
Class: |
H01M 4/131 20060101
H01M004/131; H01M 10/0525 20060101 H01M010/0525; C01G 53/00
20060101 C01G053/00 |
Goverment Interests
GOVERNMENT SUPPORT
[0001] This invention was made with government support under Grant
No. DMR-1410946 awarded by the U.S. National Science Foundation.
The Government has certain rights in the invention.
Claims
1. A silicon-modified metal oxide comprising a compound having
empirical formula
Li[Li.sub.yMn.sub..alpha.-xSi.sub.xM.sup.III.sub.bM.sup.II.sub.c-
]O.sub.2 (I) wherein y=0.01-0.33; x=0.001-0.15; a, b, and c are
each greater than zero; M.sup.III is a trivalent metal or a
combination of metals with an average valence of +3; M.sup.II is a
divalent metal or a combination of metals with an average valence
of +2; and y+4a+3b+2c is equal to 3 or about 3.
2. The silicon-modified metal oxide according to claim 1, wherein
y.gtoreq.0.02.
3. The silicon-modified metal oxide according to claim 1, wherein
y.gtoreq.0.05.
4. The silicon-modified metal oxide according to claim 1, wherein
x.gtoreq.0.02.
5. The silicon-modified metal oxide according to claim 1, wherein
x.gtoreq.0.05.
6. The silicon-modified metal oxide according to claim 1, wherein
x.gtoreq.0.07.
7. The silicon-modified metal oxide according to claim 1, wherein
M.sup.III comprises Co and M.sup.II comprises Ni.
8. The silicon-modified metal oxide according to claim 1, wherein
a>0.3.
9. The silicon-modified metal oxide according to claim 1, wherein a
is 0.3-0.67.
10. A lithium ion battery comprising an anode, a cathode, and a
separator disposed between the anode and cathode, wherein the
cathode comprises a mixed metal oxide compound according to claim
1.
11. The lithium ion battery of claim 10, wherein the mixed metal
oxide compound has an empirical Formula (II):
Li[Li.sub.0.2Mn.sub.0.49Si.sub.0.05Ni.sub.0.13Co.sub.0.13]O.sub.2
(II).
12. A method for synthesizing a silicon-modified metal oxide
according to claim 1, comprising: combining soluble salts
comprising Mn.sup.2+, Ni.sup.+2, and Co.sup.+2 in an aqueous
solution; co-precipitating hydroxide salts as solids from the
aqueous solution with base; collecting co-precipitated solids;
combining the solids with lithium hydroxide and a silicon compound;
and calcining a resulting composition in air at a temperature
sufficient to calcine the materials to make a composition according
to claim 1.
13. The method according to claim 12, wherein M.sup.III comprises
Co and M.sup.II comprises Ni.
14. The method according to claim 12, comprising calcining at a
temperature of 600-1200.degree. C.
15. The method of claim 12, wherein the silicon compound comprises
silicic acid.
16. The method of claim 12, wherein the silicon compound comprises
a siloxane or polysiloxane.
17. The method of claim 12, wherein the silicon compound is a
solid.
18. A method of operating a lithium ion battery comprising:
providing a lithium ion battery comprising an anode, a cathode, and
a separator disposed between the cathode and anode, wherein the
cathode comprises a battery active material prepared in a
discharged state; and applying a voltage difference between the
cathode and anode to de-lithiate the battery active material in the
cathode and charge the lithium ion battery, wherein the battery
active material comprises a mixed metal oxide having empirical
formula
Li[Li.sub.yMn.sub..alpha.-xSi.sub.xM.sup.III.sub.bM.sup.II.sub.c]O.sub.2
(I) wherein y=0.01-0.33; a=0.3-0.67; x=0.001-0.15; and b and c are
both greater than zero; M.sup.III is a trivalent metal or a
combination of metals with an average valence of +3; M.sup.II is a
divalent metal or a combination of metals with an average valence
of +2; and y+4a+3b+2c is equal to about +3 or about +3.
19. The method according to claim 18, wherein M.sup.III comprises
cobalt and M.sup.II comprises nickel.
20. The method of claim 18, wherein x.gtoreq.0.01 and y.gtoreq.0.1.
Description
BACKGROUND
[0002] This section provides background information related to the
present disclosure which is not necessarily prior art.
[0003] The present disclosure relates to silicon-modified
Li.sub.2MnO.sub.3--LiMO.sub.2 (M=Ni,Mn,Co) cathode material for
lithium ion batteries.
[0004] Lithium-ion batteries for battery electric vehicles (BEV)
desirably have high energy density, long life, and exhibit safety.
The cathode is an important component of the battery, because it is
the limiting factor with respect to cell energy density and hence
is a major determinant of the mass, volume, and cost of the
battery. Lithium-rich layered oxides
Li[Li.sub.x/3Mn.sub.2x/3M.sub.1-x]O.sub.2, alternatively designated
as xLi.sub.2Mn.sup.+4O.sub.3.(1-x)LiMO.sub.2 (M=Ni, Mn, Co) or
HE-NMC, are attractive candidates as cathodes for lithium-ion
batteries because they exhibit higher capacity (>250 mAh/g) and
are less expensive than other commercially available cathode
materials.
[0005] In spite of the high capacity of HE-NMC there remain
fundamental challenges preventing its commercial application. These
include voltage decay during cycling, short calendar and cycle
life, and fast resistance rise at low state of charge (SOC). These
challenges are related to the Mn-rich nature and the structural
instability of these materials induced by the oxidation of oxygen.
Indeed, considerable research has already been devoted to
understanding the structural evolution of HE-NMC materials.
SUMMARY
[0006] This section provides a general summary of the disclosure,
and is not a comprehensive disclosure of its full scope or all of
its features.
[0007] In certain variations, the present disclosure provides a
silicon-modified metal oxide including a compound having empirical
formula
Li[Li.sub.yMn.sub.a-xSi.sub.xM.sup.III.sub.bM.sup.II.sub.c]O.sub.2
(I)
wherein [0008] y=0.01-0.33; [0009] x=0.001-0.15; [0010] a, b, and c
are each greater than zero; [0011] M.sup.III is a trivalent metal
or a combination of metals with an average valence of +3; [0012]
M.sup.II is a divalent metal or a combination of metals with an
average valence of +2; and [0013] y+4a+3b+2c is equal to 3 or about
3.
[0014] In one aspect, y.gtoreq.0.02.
[0015] In one aspect, y.gtoreq.0.05.
[0016] In one aspect, x.gtoreq.0.02.
[0017] In one aspect, x.gtoreq.0.05.
[0018] In one aspect, x.gtoreq.0.07.
[0019] In one aspect, M.sup.III includes Co and M.sup.II includes
Ni.
[0020] In one aspect, a>0.3.
[0021] In one aspect, a is 0.3-0.67.
[0022] In one aspect, a lithium ion battery is provided that
includes an anode, a cathode, and a separator disposed between the
anode and cathode. The cathode includes a mixed metal oxide
compound according to any of the variations described above.
[0023] In one aspect, the mixed metal oxide has an empirical
Formula (II):
Li[Li.sub.0.2Mn.sub.0.49Si.sub.0.05Ni.sub.0.13Co.sub.0.13]O.sub.2
(II).
[0024] In one aspect, a method for synthesizing a silicon-modified
metal oxide according to any of the variations described above,
includes:
[0025] combining soluble salts including Mn.sup.2+, Ni.sup.+2, and
Co.sup.+2 in an aqueous solution;
[0026] co-precipitating hydroxide salts as solids from the aqueous
solution with base;
[0027] collecting the co-precipitated solids;
[0028] combining the solids with lithium hydroxide and a silicon
compound; and
[0029] calcining the resulting composition in air at a temperature
sufficient to calcine the materials to make a composition according
to any of the variations described above.
[0030] In one aspect, M.sup.III includes Co and M.sup.II includes
Ni.
[0031] In one aspect, the method further includes calcining at a
temperature of 600-1200.degree. C.
[0032] In one aspect, the silicon compound includes silicic
acid.
[0033] In one aspect, the silicon compound includes a siloxane or
polysiloxane.
[0034] In one aspect, the silicon compound is a solid.
[0035] In certain other variations, the present disclosure provides
a method of operating a lithium ion battery includes providing a
lithium ion battery including an anode, a cathode, and a separator
disposed between the cathode and anode. The cathode includes a
battery active material prepared in a discharged state. A voltage
difference is applied between the cathode and anode to de-lithiate
the active material in the cathode and charge the lithium ion
battery. The battery active material includes a mixed metal oxide
having empirical formula
Li[Li.sub.yMn.sub.a-xSi.sub.xM.sup.III.sub.bM.sup.II.sub.c]O.sub.2
(I)
wherein
[0036] y=0.01-0.33; a=0.3-0.67; x=0.001-0.15; and b and c are both
greater than zero;
[0037] M.sup.III is a trivalent metal or a combination of metals
with an average valence of +3;
[0038] M.sup.II is a divalent metal or a combination of metals with
an average valence of +2; and
[0039] y+4a+3b+2c is equal to about +3 or about +3.
[0040] In one aspect, M.sup.III includes cobalt and M.sup.II
includes nickel.
[0041] In one aspect, x.gtoreq.0.01 and y.gtoreq.0.1.
[0042] Further areas of applicability will become apparent from the
description provided herein. The description and specific examples
in this summary are intended for purposes of illustration only and
are not intended to limit the scope of the present disclosure.
DRAWINGS
[0043] The drawings described herein are for illustrative purposes
only of selected embodiments and not all possible implementations,
and are not intended to limit the scope of the present
disclosure.
[0044] FIGS. 1A-1C show SEM images of control
Li[Li.sub.0.2Mn.sub.0.54Ni.sub.0.13CO.sub.0.13]O.sub.2 at FIG. 1A)
3kX and FIG. 1B) 30kX magnifications; FIG. 1B) SEM image of
Li[Li.sub.0.2Mn.sub.0.49Si.sub.0.05Ni.sub.0.13Co.sub.0.13]O.sub.2
at 30kX;
[0045] FIG. 2 shows XRD patterns of pristine control, 2% Si, and 5%
Si HE-NMC powders, where an asterisk (*) indicates peaks from
Li.sub.4SiO.sub.4. The y-axis 108 shows counts (a.u.). The control
is designated 110, the 2% Si sample is designated 112, and the 5%
sample is designated 114;
[0046] FIGS. 3A-3B show Raman spectra of 3A) control, and 3B) 5% Si
HE-NMC electrodes in the pristine state, after the first charge,
and after the first discharge. In FIG. 3A, the y-axis 120 shows
intensity (a.u.) and the x-axis 122 shows wavenumber (cm.sup.-1).
Pristine is designated 130, end of charge is designated 132, and
end of discharge is designated 134. In FIG. 3B, the y-axis 140
shows intensity (a.u.) and the x-axis 142 shows wavenumber
(cm.sup.-1). Pristine is designated 150, end of charge is
designated 152, and end of discharge is designated 154;
[0047] FIG. 4 presents first cycle voltage profiles of control and
Si doped HE-NMC at C/20. The y-axis 160 shows intensity (a.u.) and
the x-axis 162 shows capacity (mAh/g). The control is designated
170, the 2% Si sample is designated 172, and the 5% sample is
designated 174;
[0048] FIG. 5 shows discharge capacity fade of control and Si doped
HE-NMC cycled at C/3. The y-axis 180 shows discharge capacity
(mAh/g) and the x-axis 182 shows cycle number. The control is
designated 190, the 2% Si sample is designated 192, and the 5%
sample is designated 194;
[0049] FIGS. 6A-6C show differential capacity plots of 6A) control,
6B) 2% Si, and 6C) 5% Si HE-NMC for every 10.sup.th cycle. In FIG.
6A, the y-axis 200 shows dQ/dV (mAh/gV) and the x-axis 202 shows
voltage (V). A first discharge is designated 210, a 12.sup.th
discharge is designated 212, a 23.sup.rd discharge is designated
214, a 34.sup.th discharge is designated 216, and a 45.sup.th
discharge is designated 218. In FIG. 6B, the y-axis 220 shows dQ/dV
(mAh/gV) and the x-axis 222 shows voltage (V). A first discharge is
designated 230, a 12.sup.th discharge is designated 232, a
23.sup.rd discharge is designated 234, a 34.sup.th discharge is
designated 236, and a 45.sup.th discharge is designated 238. In
FIG. 6C, the y-axis 240 shows dQ/dV (mAh/gV) and the x-axis 242
shows voltage (V). A first discharge is designated 250, a 12.sup.th
discharge is designated 252, a 23.sup.rd discharge is designated
254, a 34.sup.th discharge is designated 256, and a 45.sup.th
discharge is designated 258;
[0050] FIGS. 7A-7C show Nyquist plots of control and Si doped
HE-NMC at 7A) open circuit potential, 7B) the end of the first
charge, and 7C) the end of the first discharge. In FIG. 7A, the
y-axis 260 shows -1 m (.OMEGA.) and the x-axis 262 shows Re
(.OMEGA.). The control is designated 270, the 2% Si sample is
designated 272, and the 5% sample is designated 274. In FIG. 7B,
the y-axis 280 shows -1 m (.OMEGA.) and the x-axis 282 shows Re
(.OMEGA.). The control is designated 290, the 2% Si sample is
designated 292, and the 5% sample is designated 294. In FIG. 7C,
the y-axis 300 shows -1 m (.OMEGA.) and the x-axis 302 shows Re
(.OMEGA.). The control is designated 310, the 2% Si sample is
designated 312, and the 5% sample is designated 314;
[0051] FIG. 8 shows DCR measurement results during a 30 s 1 C
discharge pulse at 50% SOC for control and Si doped HE-NMC. The
y-axis 320 shows voltage (V) and the x-axis 322 shows time (s). The
control is designated 330, the 2% Si sample is designated 332, and
the 5% sample is designated 334;
[0052] FIG. 9 shows a model of first charge mechanisms for control
(right) and Si-doped (left) HE-NMC. Li[Li,M]O.sub.2(M=Ni,Co,Mn,Si)
is designated 340, as where Li[Li,M]O.sub.2(M=Ni,Co,Mn) is
designated 342. The charge to 4.4 V is designated 344, the charge
along a 4.5 V plateau is designated 346, and the end of charge is
designated 348. The oxygen vacancies in the lattice are designated
350, while the lattice densification is designated 352; and
[0053] FIG. 10 depicts an exemplary battery.
DETAILED DESCRIPTION
[0054] Layered lithium-rich positive electrode or cathode materials
xLi.sub.2MnO.sub.3.(1-x)LiMO.sub.2 (M=Mn, Co, Ni), also named high
energy NMC (HE-NMC) cathodes, have attracted considerable attention
as a promising material for lithium ion batteries thanks to their
high operating voltage (4.8 V) and specific capacity up to 280 mAh
g.sup.-1. The current teachings provide guidance how to overcome
structural instability of the HE-NMC materials, and also address a
fast resistance increase at a low stated charge using the former
materials. In one aspect, Si is used to modify the HE-NMC material
to obtain improved cathode materials for lithium ion batteries.
Synthetic methods involve incorporating Si into the lithium
manganese cobalt and nickel materials. The synthetic route results
in a stabilized cathode material structure and leads to improved
reversible capacity and reduced cell resistance.
[0055] New battery active cathode materials are provided that are
mixed oxides of Formula (I)
Li[Li.sub.yMn.sub.a-xSi.sub.xM.sup.III.sub.bM.sup.II.sub.c]O.sub.2
(I)
In Formula (I), y=0.01-0.33; a=0.3-0.67; x=0.001-0.2; a, b, c are
all greater than zero; M.sup.III is a trivalent metal or
combination of metals with an average valence of +3; M.sup.II is a
divalent metal or a combination of metals with an average valence
of +2; and y+4a+3b+2c=+3 or about +3. Thus, and y+4a+3b+2c is equal
to about +3.
[0056] In a particular embodiment, M.sup.III is cobalt and M.sup.II
is nickel. A synthetic method involves co-precipitation to form
mixed hydroxides of nickel, cobalt, and manganese. The mixed
hydroxides are collected and then dry mixed with lithium hydroxide
and a silicon compound. Finally, the dry mix, including mixed
hydroxides, of lithium hydroxide and silicon compound is heated,
for example at 900.degree. C. for a suitable time such as 12 hours
to achieve a final product having the empirical Formula
Li[Li.sub.0.2Mn.sub.0.54-xSi.sub.xNi.sub.0.13Co.sub.0.13]O.sub.2,
wherein x is a small amount relative to 0.54, and represents a
partial replacement of Mn.sup.+4 in the structure with silicon,
which is also a tetravalent (+4) element.
[0057] Thus, in certain aspects, the current teachings contemplate
silicon modified metal oxides comprising a compound describable by
the empirical Formula (I):
Li[Li.sub.yMn.sub.a-xSi.sub.xM.sup.III.sub.bM.sup.II.sub.c]O.sub.2
(I)
[0058] In Formula (I), the value of y ranges from 0.01-0.33, a is
0.3-0.67, x is from 0.001-0.2, and each of a, b, and c are greater
than 0. Further, M.sup.III is a trivalent metal or a combination of
metals having an average valence of +3, while M.sup.II is a
divalent metal or a combination of metals having average valence of
+2. Finally, the compound is charge balanced, requiring that the
sum y+4a+3b+2c be about 3. In various embodiments, the sum ranges
from about 2.8 to about 3.2, from about 2.9 to about 3.1, or from
about 2.95 to about 3.05, reflecting experimental variation,
rounding, and the like.
[0059] In further embodiments, y (which reflects an "excess" of
lithium) is greater than or equal to 0.02 or y greater than or
equal to 0.05. In various embodiments, x greater than or equal to
0.02, optionally x is greater than or equal to 0.05, or x is
greater than or equal to 0.07. In certain variations, x is from
0.001-0.15. In illustrative embodiments, M.sup.III comprises cobalt
(Co) and M.sup.II comprises nickel (Ni).
[0060] In various embodiments, the compounds of empirical Formula
(I) are manganese rich, in that a is generally greater than 0.3,
and illustratively may be in a range of about 0.3 to about 0.67,
optionally about 0.5 to about 0.67.
[0061] In other embodiments, a lithium ion battery is provided that
comprises a negative electrode or anode, a positive electrode or
cathode, and a separator disposed between the anode and cathode.
The cathode comprises a mixed metal oxide according to Formula (I).
In a particular embodiment, the active material comprises a mixed
metal oxide according to Formula (II)
Li[Li.sub.0.2Mn.sub.0.49Si.sub.0.05Ni.sub.0.13Co.sub.0.13]O.sub.2
(II)
[0062] The current teachings also provide methods for synthesizing
the compounds of Formula (I) and Formula (II) as further described.
A method for synthesizing a silicon-modified metal oxide according
to Formula (II), comprises:
[0063] combining soluble salts comprising Mn.sup.2+, Ni.sup.+2, and
Co.sup.+2 in an aqueous solution;
[0064] co-precipitating hydroxide salts as solids from the aqueous
solution with base;
[0065] collecting the co-precipitated solids;
[0066] combining the solids with lithium hydroxide and a silicon
compound; and
[0067] calcining the resulting composition in air at a temperature
sufficient to calcine the materials to make a composition according
to Formula (II).
[0068] More generally, to make compositions according to Formula
(I), stoichiometric amounts of Li, Mn, and metals making up
M.sup.II and M.sup.III are determined based on the subscripts a, b,
c, x, and y in Formula (I). First, soluble salts of Mn.sup.2+ and
other divalent metals are combined and dissolved in an aqueous
solution in the proper stoichiometric ratios. These divalent metals
include those that make up M.sup.II in the final product and those
that make up M.sup.III in the final product. To that aqueous
solution, a base (such as, without limitation, KOH) is added to
co-precipitate hydroxide salts of the metals. At this stage the
hydroxides are of metals in the +2 valence state. After
co-precipitation, the solids are collected, for example on a
filter. The solids are optionally dried and then combined and mixed
with lithium hydroxide and a silicon compound. Finally, the mixture
of hydroxides and silicon compound are calcined in air at a
temperature sufficient to calcine the materials and make a
composition according to Formula (I) or Formula (II).
[0069] The metals for the synthesis are selected to include
Mn.sup.2+, which undergoes oxidation to a valence of +4; a metal or
group of metals that changes from a valence state of +2 to a
valence state of +3, and a metal or group of metals that remains
unchanged with a valence state of +2. It is believed that the
calcining conditions lead to these valence changes. In an exemplary
embodiment, the synthetic conditions change Mn.sup.+2 to Mn.sup.+4,
and change Co.sup.+2 to Co.sup.+3 while lithium remains at +1 and
Si remains at +4 throughout the synthesis steps. In this way
Mn.sup.+4, M.sup.III, M.sup.II, L.sup.+1, and Si.sup.+4 are
incorporated into compounds of Formula (I) or Formula (II).
[0070] The stoichiometry of the starting materials is selected to
provide the mixed metal compounds illustrated in Formulas (I) and
(II), taking account of the values of the variables y, x, a, b, and
c. Notwithstanding, in some embodiments the lithium starting
material is provided at a slight surplus over that suggested by its
subscript y in Formulas (I) and (II), for example at or over an
excess of 3% relative to the other starting materials. In
particular embodiments, M.sup.III is cobalt or a mixture of metals
including cobalt, and/or M.sup.II is nickel or a combination of
elements including nickel.
[0071] The materials are calcined in air at a temperature
sufficient to form the compounds. In various embodiments, the
calcining conditions are sufficient to produce compounds wherein Mn
is found in the +4 valence state and Co is found in the +3 valence,
while Ni remains in the +2 state, unchanged from its starting
value. To accomplish this, the materials are calcined in air at a
suitable temperature such as about 600 to about 1200.degree. C.
[0072] In the compounds and in the methods to make the compounds,
silicon is provided at a low amount as a partial replacement for
the +4 valence metal, illustrated in Formulas (I) and (II) as
Mn.sup.+4. Thus, the magnesium rich materials are characterized by
the variable "a" being present at a range of greater than or equal
to 0.3, optionally greater than or equal to 0.4, or a greater than
or equal to 0.5. In certain aspects, "a" may be greater than or
equal to about 0.3 to less than or equal to about 0.67. The amount
of silicon (Si), reflected by the variable "x" is selected to be a
minor amount of the manganese fraction "a." As detailed above, "x"
may range from about 0.001 on the low end up to about 0.15 or about
0.2. In general, when the level "a" of Mn is in the lower end of
its range of 0.3 to 0.67, the values of x are in the lower end of
its range of 0.001 to 0.2. Conversely, when Mn is in the upper end
of its range, so are the values of x for the amount of Si. In
effect, the Si is incorporated into the structure of Formula (I)
only at a small fractional percentage of the Mn in the structure,
which it partially replaces. At these low levels it is believed the
Si may even occupy the Mn sites in the crystalline material. As the
Si level is increased, a point is reached at which the silicon
doped material begins to show inhomogeneous Si distribution with
microscopy. The observed material could be excess silicate material
above what can be incorporated into Formula (I).
[0073] In non-limiting embodiments, x is 0.01, 0.02, 0.05, 0.07,
0.1, or 0.15. Essentially, a small portion of the manganese is
substituted with silicon, which is another +4 material, but one
which is not lithium active. The silicon compound may be a solid,
and can be selected from silicic acid, without limitation. Other
suitable silicon compounds include siloxanes, including silicon
polymers such as polysiloxanes.
[0074] The battery active materials described herein are
synthesized in a fully discharged state. Accordingly, a method for
operating a lithium ion battery involves providing the battery with
a cathode, anode and separator disposed between them, wherein the
cathode comprises a battery active material prepared in discharged
state according to the formulas set forth herein and the methods
described. A voltage difference is supplied between the cathode and
the anodes to de-lithiate the active material and charge the
lithium ion battery.
[0075] Thus in one aspect, the current teachings are concerned with
the choice of element being incorporated into the
Li.sub.2MnO.sub.3--LiMO.sub.2 (M=Ni,Mn,Co) material and the method
of synthesis to stabilize the cathode material's crystal structure
and decrease the cathode's resistance for improved Li-ion battery
performance.
[0076] With reference to FIG. 10, the present teachings generally
relate to high energy NMC materials subjected to silicon doping or
silicon modifying to provide a battery active material having
superior capacity relative to a control without silicon. In various
embodiments, the silicon modified HE-NMC materials are used as part
of a battery 100 as generically depicted in FIG. 10. The battery
100 includes the anode 102, a cathode 104, and a separator 106
containing electrolyte. While the battery of FIG. 10 is a
simplified illustration, the electrode of the current teachings can
be used as a cathode material in all lithium based batteries using
metallic lithium or alternative anodes such as carbonaceous and
graphitic anodes, lithium alloys, silicon based alloys, oxides,
nitrides, phosphides, borides, and so on.
[0077] While various aspects of the inventive technology have been
described with reference to various example embodiments, further
non-limiting disclosure is given in the example section that
follows.
EXAMPLES
[0078] Synthesis
[0079] Li[Li.sub.0.2Mn.sub.0.54Ni.sub.0.13Co.sub.0.13]O.sub.2
powders were synthesized by a co-precipitation method. The reactant
quantities were calculated to give a
Li.sub.12Mn.sub.0.54Ni.sub.0.13Co.sub.0.13O.sub.2 control
stoichiometry, with 3% excess lithium. Dopant quantities were
calculated to substitute manganese at 2 and 5% doping levels,
yielding
Li[Li.sub.0.2Mn.sub.0.52Si.sub.0.02Ni.sub.0.13CO.sub.0.13]O.sub.2
(2% Si, where x=0.02) and
Li[Li.sub.0.2Mn.sub.0.49Si.sub.0.05Ni.sub.0.13CO.sub.0.13]O.sub.2
(5% Si, where x=0.05), respectively. Manganese sulfate tetrahydrate
(Sigma Aldrich), cobalt sulfate septahydrate (Sigma Aldrich), and
nickel sulfate hexahydrate (Sigma Aldrich) precursors were dripped
into a potassium hydroxide (Baker) solution and the precipitate was
filtered, washed with deionized water, and dried in an 80.degree.
C. oven overnight. Lithium hydroxide and silicic acid (Sigma
Aldrich) were measured and ground with the dried transition metal
precipitate using a mortar and pestle for 30 minutes. The ground
powder was placed in a crucible and calcined in a furnace at
900.degree. C. for 12 hours.
[0080] Material Characterization
[0081] The structure was determined using X-ray powder diffraction
measurements made on a Bruker D8 Advance with Cu K-alpha radiation
in the 20 theta range of 10.degree. to 90.degree. at a step rate of
0.01.degree./s. Scanning electron microscopy (SEM) images were
conducted to investigate the morphology of the material. Electrode
powders were attached to the aluminum stub using two-sided
conductive carbon tape. A conductive gold-palladium alloy was
sputter deposited onto the powders for 8 seconds using a Denton 11
sputter deposition system. Images were obtained using a Hitachi
s-4800 SEM with 5 kV accelerating voltage, 5 mm working distance
and the inlens detector. A Thermoscientific Nicolet Almega XR
dispersive Raman was used with a 532 nm wavelength source,
20.times. objective and 100 .mu.m aperture to characterize
structural changes in electrodes at various points in the first
cycle ex situ. Two samples per condition and two locations per
sample were analyzed. To ensure the beam was not damaging the
sample and changing the signal, the same location on the same
sample was collected twice and the response was unchanged.
[0082] Electrochemical Characterization
[0083] Slurries were made with an 80:10:10 formulation of active
material to PVDF binder (Kynar) to Super P conductive carbon
(Timcal) in 1-methyl-2-pyrrolidone (Sigma Aldrich) mixed in a
Thinky planetary mixer. Electrodes were made by coating the slurry
on aluminum foil with a wet 10 mil drawdown bar, dried in an
80.degree. C. oven overnight, and stored in the oven until ready
for use. Electrodes were punched to a 12.7 mm diameter. Al-clad
CR2032-type coin cells were assembled in an argon filled glovebox
(Vacuum Atmospheres Co.) using Li counter electrode, 3/4'' diameter
Cellgard 2325, and 150 .mu.l of 1M LiPF.sub.6 1/1 (vol.) EC/EMC
(BASF) electrolyte. Electrochemical testing was performed at
30.degree. C. using Maccor 4000 series battery cyclers. Samples
were cycled with an initial C/20 rate followed two cycles at C/10,
then C/3 cycling in a 2-4.6 V vs. Li/Li.sup.+ voltage window, where
the 1 C current depends on the active material mass and averages 2
mA. Differential capacity measurements were conducted at a C/100
rate. Direct Current Resistance (DCR) is a useful tool to assess
batteries for electric vehicle applications. In the DCR
measurement, cells were discharged at C/20 to 50% state of charge
(SOC), allowed to rest one hour, and discharged at 1 C for 30 s. AC
impedance spectra were recorded with a Biologic VMP3 in the 1
MHz-10 mHZ range with 10 points per decade. Cells were built in
duplicate or triplicate to confirm consistency of electrochemical
performance. Cells were disassembled and cleaned in dimethyl
carbonate (BASF) before postmortem characterization.
[0084] Results and Discussion
[0085] Material Characterization
[0086] Li[Li.sub.0.2Mn.sub.0.54Ni.sub.0.13Co.sub.0.13]O.sub.2
synthesized by the co-precipitation method results in large
secondary particle agglomerations as seen in FIG. 1A, with primary
particles approximately 100 nm in diameter (FIG. 1B). The small
particle size reduces the Li+ diffusion distance, facilitating
lithium extraction and insertion during electrochemical cycling.
The morphology did not change with Si doping (FIG. 1C).
[0087] FIG. 2 shows XRD patterns of pristine control, 2% Si (where
x is 0.02), and 5% Si (where x is 0.05) HE-NMC powders, where an
asterisk (*) indicates peaks from Li.sub.4SiO.sub.4. The y-axis 108
shows counts (a.u.). The control is designated 110, the 2% Si
sample is designated 112, and the 5% sample is designated 114. All
sample patterns match the .alpha.-NaFeO.sub.2 type layered
structure (R3m space group). The 5% Si HE-NMC pattern shows trace
amount of Li.sub.4SiO.sub.4, indicated with asterisks. The small
reflection peaks around 2.theta.=20.degree. correspond to cation
ordering in the transition metal layer in the Li.sub.2MnO.sub.3
phase, belonging to the C2/m space group. Splitting of the
(006/012) and (018)/(110) peaks indicates the samples have highly
ordered layered structures. Table 1 lists the lattice parameters of
the three HE-NMC samples obtained from Rietveld refinements. The a
and c parameters increase as the Si doping level increases, as
observed in Si-doped LiNi.sub.xMn.sub.yCo.sub.1-x-yO.sub.2.
Furthermore, the a/c ratio increases with the doping level,
suggesting that Si doping improves the layered structure.
TABLE-US-00001 TABLE 1 Lattice parameters of HE-NMC samples from
Rietveld refinement of the rhombohedral phase. Sample a (.ANG.) c
(.ANG.) c/a Control 2.8502 14.2234 4.9903 2% Si 2.8515 14.2313
4.9908 5% Si 2.8524 14.2448 4.9940
[0088] Raman is sensitive to small structure changes at the surface
in nanoparticles, where the surface is volumetrically large. FIG.
3A shows the Raman spectra of control HE-NMC in the pristine
condition, at the end of the first charge, and at the end of the
first discharge. The pristine sample has a peak at 420 cm.sup.-1
corresponding to Li.sub.2MnO.sub.3, 470 cm.sup.-1 from E.sub.g in
plane metal-oxygen vibrations, and 590 cm.sup.-1 corresponding to
the A.sub.1g transverse metal oxygen vibrations. By the end of the
first charge the E.sub.g and A.sub.1g peaks have shifted to higher
wavenumber and the peak from Li.sub.2MnO.sub.3 has disappeared. The
blue shift of the metal-oxygen vibrations is indicative of
spinel-like ordering.
[0089] FIG. 2 shows XRD patterns of pristine control, 2% Si, and 5%
Si HE-NMC powders, where an asterisk (*) indicates peaks from
Li.sub.4SiO.sub.4. The y-axis 108 shows counts (a.u.). The control
is designated 110, the 2% Si sample is designated 112, and the 5%
sample is designated 114;
[0090] FIGS. 3A-3B show Raman spectra of 3A) control, and 3B) 5% Si
RE-NMC electrodes in the pristine state, after the first charge,
and after the first discharge. In FIG. 3A, the y-axis 120 shows
intensity (a.u.) and the x-axis 122 shows wavenumber (cm.sup.-1).
Pristine is designated 130, end of charge is designated 132, and
end of discharge is designated 134. FIG. 3B shows the Raman spectra
for 5% Si doped HE-NMC at the same three conditions. In FIG. 3B,
the y-axis 140 shows intensity (a.u.) and the x-axis 142 shows
wavenumber (cm.sup.-1). Pristine is designated 150, end of charge
is designated 152, and end of discharge is designated 154. Table 2
includes the position of the A.sub.1g peak for samples at the three
conditions. As the doping level increases the peak position is
maintained. This suggests that doping mitigates the structure
change without compromising capacity or limiting activation.
TABLE-US-00002 TABLE 2 Raman A.sub.1g peak position evolution over
the first cycle. A.sub.1g Peak Position (cm.sup.-1) Sample Pristine
End of Charge End of Discharge Control 590 610 610 2% Si 595 595
610 5% Si 590 590 600
[0091] Electrochemical Performance
[0092] The voltage profiles from the first cycle of the synthesized
materials can be seen in FIG. 4. FIG. 4 presents first cycle
voltage profiles of control and Si doped HE-NMC at C/20. The y-axis
160 shows intensity (a.u.) and the x-axis 162 shows capacity
(mAh/g). The control is designated 170, the 2% Si sample is
designated 172, and the 5% sample is designated 174. The first
charge profile is characterized by a large plateau around 4.5V. The
discharge capacity of 5% Si doped HE-NMC is 253 mAh/g compared to
227 mAh/g for the control. The Si-doped samples have a prolonged
sloping component, reaching the plateau at a higher capacity than
the control. The overpotential of the Si-doped samples are reduced.
FIG. 5 shows the higher discharge capacity of the 5% Si doped
samples is maintained over forty cycles at C/3. The y-axis 180
shows discharge capacity (mAh/g) and the x-axis 182 shows cycle
number. The control is designated 190, the 2% Si sample is
designated 192, and the 5% sample is designated 194. The larger
lattice could lead to the observed higher capacity by increasing
Li.sup.+ ion mobility.
[0093] The evolution in the voltage profiles can easily be seen in
the differential capacity plot in FIGS. 6A-6C for the 1.sup.st,
12.sup.th, 23.sup.rd, 34.sup.th, and 45.sup.th cycle. In FIG. 6A,
the y-axis 200 shows dQ/dV (mAh/gV) and the x-axis 202 shows
voltage (V). A first discharge is designated 210, a 12.sup.th
discharge is designated 212, a 23.sup.rd discharge is designated
214, a 34.sup.th discharge is designated 216, and a 45.sup.th
discharge is designated 218. In FIG. 6B, the y-axis 220 shows dQ/dV
(mAh/gV) and the x-axis 222 shows voltage (V). A first discharge is
designated 230, a 12.sup.th discharge is designated 232, a
23.sup.rd discharge is designated 234, a 34.sup.th discharge is
designated 236, and a 45.sup.th discharge is designated 238. In
FIG. 6C, the y-axis 240 shows dQ/dV (mAh/gV) and the x-axis 242
shows voltage (V). A first discharge is designated 250, a 12.sup.th
discharge is designated 252, a 23.sup.rd discharge is designated
254, a 34.sup.th discharge is designated 256, and a 45.sup.th
discharge is designated 258. The first charge has anodic peaks from
Ni.sup.2+/.sup.4+ and Co.sup.3+/.sup.4+ oxidation around 4V and a
peak at the plateau around 4.5V. The anodic shoulder at 3.25V
shifts to lower voltages with increasing cycle number, whereas the
peaks around 3.6V and 3.8V shift to higher voltages with increasing
cycle number. The discharge has cathodic peaks around 3.7V from
Ni.sup.4+/.sup.2+ and Co.sup.4+/.sup.3+ reduction and a peak at 3V
from the development of a spinel-like phase.sup.3,17. The peaks
around 3.7V and 3V shift to lower voltages, where the peak at 3V
grows with cycle number while the peak at 3.7V shrinks. In the
control material, the Mn.sup.4+/.sup.3+ reduction peaks become more
intense with cycling as the Ni.sup.4+/.sup.2+ and Co.sup.4+/.sup.3+
reductions grow inactive. The 3V discharge peak of the Si doped
HE-NMC is more stable than that of the control sample, indicating
less spinel-like formation.
[0094] Resistance Measurements
[0095] EIS measurements are used to separate contributions to the
internal resistance in cells. FIG. 7A shows the impedance spectra
after a 12-hour rest at the open circuit potential (OCP). In FIG.
7A, the y-axis 260 shows -1 m (.OMEGA.) and the x-axis 262 shows Re
(.OMEGA.). The control is designated 270, the 2% Si sample is
designated 272, and the 5% sample is designated 274. The high
frequency semicircle provides information on the surface reactions
and contact resistance in the cell, and the mid frequency region is
related to charge transfer resistance at the electrode-electrolyte
interface. The line in the low frequency region contains
information on solid state diffusion and is referred to as the
Warburg impedance. In FIG. 7A the ohmic resistance is similar among
all samples, and the Si containing samples have larger semicircle
diameters, corresponding to higher surface and interfacial
resistances. These semicircles are overlapping, thus this
qualitative analysis will not attempt to separate out the
contributions from surface reactions and interfacial charge
transfer resistances. The impedance spectra at the end of the first
charge to 4.6 V is shown in FIG. 7B. In FIG. 7B, the y-axis 280
shows -1 m (.OMEGA.) and the x-axis 282 shows Re (.OMEGA.). The
control is designated 290, the 2% Si sample is designated 292, and
the 5% sample is designated 294. The control sample has a
significantly higher ohmic resistance relative to the Si doped
samples. This could be due to more oxygen release from surface
changes in the control samples, changing the resistance of the
electrolyte. The surface and interfacial resistances are also much
higher in the control material, indicating a higher electrolyte
reactivity. Si doping may help stabilize the electrolyte-electrode
interface by lowering the interfacial resistance. HE-NMC is known
to have high resistance at low states of charge, which is
problematic for applications requiring pulse power capability.
These findings suggest that Si doping lowers the resistance of
HE-NMC. FIG. 7C shows the impedance spectra after the first
discharge is similar for all samples. In FIG. 7C, the y-axis 300
shows -1 m (.OMEGA.) and the x-axis 302 shows Re (.OMEGA.). The
control is designated 310, the 2% Si sample is designated 312, and
the 5% sample is designated 314.
[0096] Direct Current Resistance (DCR) is a practical measure of
internal resistance. It is collected using 1 C pulses at 50% SOC
during the first discharge. FIG. 8 shows the voltage response
during the 30 second pulse for the control, 2% Si (where x is
0.02), and 5% Si HE-NMC (where x is 0.05) samples. FIG. 8 shows DCR
measurement results during a 30 s 1 C discharge pulse at 50% SOC
for control and Si doped HE-NMC. The y-axis 320 shows voltage (V)
and the x-axis 322 shows time (s). The control is designated 330,
the 2% Si sample is designated 332, and the 5% sample is designated
334. The voltage drop can has two regimes, the first regime is the
ohmic drop and occurs in the first second of the pulse step. As the
doping level increases, the slope of the first regime segment
decreases. The ohmic drop decreases with increased doping levels,
supporting our impedance findings that Si doping reduces
resistance.
[0097] Accordingly, HE-NMC can be successfully doped with Si using
a co-precipitation synthetic method. At 5% Si doping levels trace
amounts of a second phase was visible. The Si doped material shows
increased capacity, with 5% Si HE-NMC having a 10% higher discharge
capacity relative to the control. Because Si is not lithium active,
the initial capacity was expected to be lower than the control.
However, the larger lattice parameters and lower electrochemical
impedance associated with Si doping may in fact have contributed to
the increased capacity by making lithium extraction easier. Si
doping likely changes the site energy to suppress Mn--O octahedral
collapse and leads to less local structural change during
activation.
[0098] The Raman results indicate that Si doping mitigates
structural changes during the first cycle. EIS measurements show
that the charge transfer resistance is much lower in the Si doped
samples. DCR measurements at 50% SOC support this finding. The
lower resistance of Si doped materials is consistent with the lower
overpotential in the first charge voltage profile. The control
sample has the highest resistance and reaches the activation
plateau first.
[0099] Although the current teachings are not to be limited by
theoretical considerations, FIG. 9 shows a model for a possible
explanation of the increased capacity of Si doped HE-NMC.
Li[Li,M]O.sub.2(M=Ni,Co,Mn,Si) is designated 340, as where
Li[Li,M]O.sub.2(M=Ni,Co,Mn) is designated 342. The charge to 4.4 V
is designated 344, the charge along a 4.5 V plateau is designated
346, and the end of charge is designated 348. The oxygen vacancies
in the lattice are designated 350, while the lattice densification
is designated 352. In both materials, initial charging to 4.4V
oxidizes the transition metal ions and creates lithium and
transition metal vacancies in the material. Along the plateau, more
lithium is extracted by creating oxygen vacancies. In the Si-doped
material (left), the oxygen vacancies hop but stay in the bulk. In
the control material (right), the oxygen vacancies created at the
surface are removed from the structure and the transition metal
ions migrate to the bulk. By the end of the charge, the Si doped
material has oxygen vacancies embedded within the lattice while the
control material exhibits lattice densification.
[0100] The present teachings show that Si doping increases the
capacity of HE-NMC and is attributed to the increased lattice
parameters and lowered resistance during the first cycle.
[0101] Example embodiments are provided so that this disclosure
will be thorough, and will fully convey the scope to those who are
skilled in the art. Numerous specific details are set forth such as
examples of specific compositions, components, devices, and
methods, to provide a thorough understanding of embodiments of the
present disclosure. It will be apparent to those skilled in the art
that specific details need not be employed, that example
embodiments may be embodied in many different forms and that
neither should be construed to limit the scope of the disclosure.
In some example embodiments, well-known processes, well-known
device structures, and well-known technologies are not described in
detail.
[0102] The terminology used herein is for the purpose of describing
particular example embodiments only and is not intended to be
limiting. As used herein, the singular forms "a," "an," and "the"
may be intended to include the plural forms as well, unless the
context clearly indicates otherwise. The terms "comprises,"
"comprising," "including," and "having," are inclusive and
therefore specify the presence of stated features, elements,
compositions, steps, integers, operations, and/or components, but
do not preclude the presence or addition of one or more other
features, integers, steps, operations, elements, components, and/or
groups thereof. Although the open-ended term "comprising," is to be
understood as a non-restrictive term used to describe and claim
various embodiments set forth herein, in certain aspects, the term
may alternatively be understood to instead be a more limiting and
restrictive term, such as "consisting of" or "consisting
essentially of" Thus, for any given embodiment reciting
compositions, materials, components, elements, features, integers,
operations, and/or process steps, the present disclosure also
specifically includes embodiments consisting of, or consisting
essentially of, such recited compositions, materials, components,
elements, features, integers, operations, and/or process steps. In
the case of "consisting of," the alternative embodiment excludes
any additional compositions, materials, components, elements,
features, integers, operations, and/or process steps, while in the
case of "consisting essentially of," any additional compositions,
materials, components, elements, features, integers, operations,
and/or process steps that materially affect the basic and novel
characteristics are excluded from such an embodiment, but any
compositions, materials, components, elements, features, integers,
operations, and/or process steps that do not materially affect the
basic and novel characteristics can be included in the
embodiment.
[0103] Any method steps, processes, and operations described herein
are not to be construed as necessarily requiring their performance
in the particular order discussed or illustrated, unless
specifically identified as an order of performance. It is also to
be understood that additional or alternative steps may be employed,
unless otherwise indicated.
[0104] When a component, element, or layer is referred to as being
"on," "engaged to," "connected to," or "coupled to" another element
or layer, it may be directly on, engaged, connected or coupled to
the other component, element, or layer, or intervening elements or
layers may be present. In contrast, when an element is referred to
as being "directly on," "directly engaged to," "directly connected
to," or "directly coupled to" another element or layer, there may
be no intervening elements or layers present. Other words used to
describe the relationship between elements should be interpreted in
a like fashion (e.g., "between" versus "directly between,"
"adjacent" versus "directly adjacent," etc.). As used herein, the
term "and/or" includes any and all combinations of one or more of
the associated listed items.
[0105] Although the terms first, second, third, etc. may be used
herein to describe various steps, elements, components, regions,
layers and/or sections, these steps, elements, components, regions,
layers and/or sections should not be limited by these terms, unless
otherwise indicated. These terms may be only used to distinguish
one step, element, component, region, layer or section from another
step, element, component, region, layer or section. Terms such as
"first," "second," and other numerical terms when used herein do
not imply a sequence or order unless clearly indicated by the
context. Thus, a first step, element, component, region, layer or
section discussed below could be termed a second step, element,
component, region, layer or section without departing from the
teachings of the example embodiments.
[0106] Spatially or temporally relative terms, such as "before,"
"after," "inner," "outer," "beneath," "below," "lower," "above,"
"upper," and the like, may be used herein for ease of description
to describe one element or feature's relationship to another
element(s) or feature(s) as illustrated in the figures. Spatially
or temporally relative terms may be intended to encompass different
orientations of the device or system in use or operation in
addition to the orientation depicted in the figures.
[0107] Throughout this disclosure, the numerical values represent
approximate measures or limits to ranges to encompass minor
deviations from the given values and embodiments having about the
value mentioned as well as those having exactly the value
mentioned. Other than in the working examples provided at the end
of the detailed description, all numerical values of parameters
(e.g., of quantities or conditions) in this specification,
including the appended claims, are to be understood as being
modified in all instances by the term "about" whether or not
"about" actually appears before the numerical value. "About"
indicates that the stated numerical value allows some slight
imprecision (with some approach to exactness in the value;
approximately or reasonably close to the value; nearly). If the
imprecision provided by "about" is not otherwise understood in the
art with this ordinary meaning, then "about" as used herein
indicates at least variations that may arise from ordinary methods
of measuring and using such parameters. For example, "about" may
comprise a variation of less than or equal to 5%, optionally less
than or equal to 4%, optionally less than or equal to 3%,
optionally less than or equal to 2%, optionally less than or equal
to 1%, optionally less than or equal to 0.5%, and in certain
aspects, optionally less than or equal to 0.1%.
[0108] In addition, disclosure of ranges includes disclosure of all
values and further divided ranges within the entire range,
including endpoints and sub-ranges given for the ranges.
[0109] Example embodiments will now be described more fully with
reference to the accompanying drawings.
[0110] The foregoing description of the embodiments has been
provided for purposes of illustration and description. It is not
intended to be exhaustive or to limit the disclosure. Individual
elements or features of a particular embodiment are generally not
limited to that particular embodiment, but, where applicable, are
interchangeable and can be used in a selected embodiment, even if
not specifically shown or described. The same may also be varied in
many ways. Such variations are not to be regarded as a departure
from the disclosure, and all such modifications are intended to be
included within the scope of the disclosure.
* * * * *